Question

during a trip to the galapagos islands, which observation led charles darwin to suspect that organisms change over time?
island finches were able to breed with mainland species.
island finches resembled mainland finches, but were not the same species.
island finches resembled extinct species from other islands around the world.
island finches did not have beaks of the same size and shape.

Explanation:

Darwin observed that island finches resembled mainland finches but were distinct species. This suggested that they had evolved from a common ancestor. Breeding ability (if they were different species, they likely couldn't breed freely), resemblance to extinct species from other islands (not the key observation for evolution over time in this context), and beak size/shape (a result of evolution but the core was the species - level resemblance and difference) are less relevant.

Answer:

Island finches resembled mainland finches, but were not the same species.